Most currently available pressure sensitive adhesive emulsions do not meet the performance requirements for vinyl applications in the adhesive market. Most of the adhesive products that are presently used for vinyl applications are solvent based. Needless to say the use of solvent based adhesives leads to environmental and workplace emissions problems.
For a pressure sensitive adhesive to be suitable for vinyl applications, i.e. the base stock is polyvinyl chloride which is most likely plasticized, the copolymer adhesive must have the following properties:
loop tack of greater than 1.5 pli (pounds per linear inch),
24 hour peel adhesion buildup of at least about 4 pli,
high cohesive strength of at least 30 hours (PSTC-7) standard creep resistance, and
suitable moisture resistance.
Of particular importance is the need for greater than about 4 pli peel adhesion buildup, for otherwise the vinyl base stock will peel off the substrate. Permanency is needed so that the vinyl base stock will be destroyed rather than peel off the substrate.
In the pressure sensitive adhesive art, cohesive strength is measured by shear strength or shear (creep) resistance, which is the resistance of adhesive joints to shear stresses and is measured as the force per unit area sheared at failure. Shear is parallel to the adhesive joint.
Peel or peel strength is measured by drawing an adhesive applied to a substrate at some angle to the substrate, usually 90.degree. or 180.degree..
Tack or loop tack is the resistance offered by the adhesive film to detachment from an adhered surface. It is a measure of stickiness of an adhesive, or the ability to form an instant bond when brought into contact with a substrate to which adhesive is to be adhered.
Although many attempts have been made to enhance the shear strength of adhesive polymers, the tack and peel values of the resulting adhesive generally lessen with an increase in shear strength.
European Patent Application 0 225 541 discloses pressure sensitive adhesives comprising terpolymers of ethylene, vinyl acetate and di-2-ethylhexyl maleate or di-n-octyl maleate or the corresponding fumarate.
DE 3,531,601 discloses an aqueous pressure sensitive emulsion whose polymer comprises
(a) 40-89 wt % vinyl ester,
(b) 10-45 wt % ethylene,
(c) 0.5-4 wt % unsaturated carboxylic and,
(d) 0.5-10 wt % hydroxyalkyl acrylate,
(e) 0-25 wt % alkyl acrylate, and
(f) 0-10 wt % ethylenically mono-unsaturated or polyunsaturated comonomers.
U.S. Pat. No. 4,322,516 discloses pressure sensitive adhesive emulsion copolymers comprising
(a) 10-30 wt % ethylene,
(b) 29-69 wt % acrylic acid esters of alcohols,
(c) 20-55 wt % vinyl acetate,
(d) 0.2-8 wt % (meth)acrylamide, and
(e) 0-12 wt % other olefinically unsaturated comonomers.
U.S. Pat. No. 4,507,429 discloses a pressure sensitive adhesive composition comprising a polymer of an acrylate ester and/or vinyl ester, an olefinically unsaturated carboxylic acid comonomer, and a polyolefinically unsaturated comonomer. The acrylate ester may be a diester of an alpha, beta-olefinically unsaturated dicarboxylic acid.
U.S. Pat. No. 4,564,664 discloses pressure sensitive adhesives which are polymers of a diester of fumaric acid, an alkyl acrylate, an alkyl methacrylate and, desirably, a crosslinkable carboxylic acid.
U.S. Pat. No. 4,702,957 discloses an aqueous emulsion for bonding nonwoven fabrics containing a vinyl ester, 10-30 wt % ethylene, 15-40 wt % dialkyl maleate and 1-5 wt % N-methylol containing comonomer.
U.S. Pat. No. 3,563,944 discloses the copolymerization of vinyl acetate with acrylates, acrylic acid, maleates and fumarates to provide an emulsion especially useful in a paint formulation.
U.S. Pat. No. 3,257,478 discloses pressure sensitive adhesives comprising vinyl acetate. octyl acrylate, ethyl acrylate and maleic anhydride. In addition, crosslinkable monomers such as N-methylolacrylamide are included.
U.S. Pat. No. 3,654,213 discloses a pressure sensitive adhesive comprising a polymer base of 2-ethylhexyl acrylate, vinyl acetate, acrylic acid and a mixed vinyl ester of an alkanoic acid containing 10-12 carbon atoms.
U.S Pat. No. 3,697,618 discloses an acrylic pressure sensitive adhesive consisting of a vinyl ester of a saturated monocarboxylic acid, e.g. vinyl acetate, and an alpha,beta-ethylenically unsaturated dicarboxylic acid.
U.S. Pat. No. 3,890,292 discloses a pressure sensitive adhesive comprising an alkyl acrylate, an alpha,beta-unsaturated carboxylic acid such as acrylic acid, a vinyl ester, e.g. vinyl acetate, and a plasticizer such as dibutyl phthalate. Emulsion polymerization techniques are employed.
U.S. Pat. No. 4,185,050 discloses a pressure sensitive adhesive comprising a terpolymer of an alkyl acrylate, a vinyl ester and an ethylenically unsaturated carboxylic acid.